Just hours earlier, in an emotional goodbye to the faithful, he declared himself a mere "pilgrim" in his final public appearance as Pope.

He arrived at the villa at the lakeside town to find a 7,000-strong crowd gathered in the main square waving yellow and white paper pennants in Vatican colours to greet him.

There were huge cheers as he briefly stepped out onto the main balcony, wearing a white robe, and spoke to the faithful with a final apostolic blessing.

"I am very happy to be here with you, surrounded by the beauty of the world. Thank you for your friendship and your affection," he said.

"You know that this day of mine has been so different from many others.

"I am no longer Pope from 8pm this evening. I am just a pilgrim on his last leg of his pilgrimage on this earth.

"I would like to work to work for the good of the Church and for humanity with my heart, faith, love, reflection and interior strength, and I feel supported with your kindness."

He went on to say: "From the bottom of my heart I bless you ... Thank you and goodnight."

Balloons spelling out his name were strung up across a shop window and banners thanking Benedict for his service were held aloft.

Earlier, he left the Vatican for the final time as leader of the Catholic Church, pledging "unconditional reverence and obedience" to whoever succeeds him.

He gave thanks to his closest aides who have been by his side during his papacy in an emotional parting ceremony, before stepping out from his apartments for the last time. Many of his staff had tears in their eyes.

As he bid the Vatican farewell as the Pope, he tweeted: "Thank you for your love and support. May you always experience the joy that comes from putting Christ at the centre of your lives."

Staff lined the route of his motorcade and applauded as the 85-year-old was driven to the Vatican helipad.

There he boarded a white Italian air force helicopter emblazoned with the Vatican flag and was flown in a spectacular journey over Rome to Castel Gandolfo - the papal summer residence on the outskirts of the city.

He is expected to spend the first two months of his retirement at the complex of villas boasting lush gardens, a farm and stunning views over Lake Albano in the volcanic crater below the town - before he retreats from public life for good.

The bells of St Peter's Basilica and churches rang out as the helicopter circled Vatican City against a backdrop of the Rome city skyline and golden setting sun.

Every minute of Benedict's departure was shown by Vatican television, including live pictures from the helicopter, as it flew over the Colosseum and other iconic landmarks.

It came 17 days after Benedict shocked the world when he announced he no longer felt mentally or physically able to continue as the 264th successor to St Peter. It broke centuries of precedent in which it became traditional for only death to end a pope's reign.

Earlier on Thursday, more than 100 cardinals said their personal farewells to Benedict at a gathering in the Clementine Hall in the Apostolic Palace.

In an unexpected speech, he urged them to stay united behind his successor.

He told them: "Among you there is the future pope, to whom I today declare my unconditional reverence and obedience."

Benedict will eventually move into the newly renovated Mater Ecclesiae Monastery of cloistered nuns inside the Vatican.

A total of 115 cardinals are expected to elect his successor in the secretive conclave process in the next few weeks, with the aim of having a new pope installed in office by Easter.